This project will examine the covalent structures of the amino acyl-tRNA synthetases; it will concentrate on a representative of this family of enzymes, isoleucyl-tRNA synthetase of E. coli. In the coming year chemical modifications of the protein will be emphasized as a means of identifying functional groups essential for catalysis and substrate binding, and to define the topography of the active site. Labeled polypeptides derived from the active site region of the protein will be isolated and sequenced. The amino acid sequence surrounding the lysine which reacts with pyridoxal 5'-phosphate will be determined. The group reacting with the affinity labeling reagent Cibiacron blue F3GA will be identified and its surrounding amino acid sequence determined. It is hoped that these studies will identify catalytic residues, lead to an insight on the enzyme mechanism, and shed light on the nature of protein-nucleic acid interactions. BIBLIOGRAPHIC REFERENCES: "Isolation of Amino Acyl-tRNA Synthetases by Affinity Chromatography on Blue Dextran-Sepharose", J. Moe and D. Piszkiewicz, Fed. Proc., 35, 1467 (1976). "Isolation of Amino Acyl Transfer Ribonucleic Acid Synthetase by Affinity Chromatography on Blue Dextran-Sepharose", J. Moe and D. Piszkiewicz, FEBS Letters, 72, 147 (1976).